Homing depth bomb for searching for an underwater target

ABSTRACT

A vertically searching depth bomb-torpedo is disclosed having at least four passive, side looking hydrophones for searching each horizontal layer of water and determining the approximate direction of a target during the vertical dive of the torpedo and a set of forward-looking hydrophones for conducting a snaking search when the torpedo pulls out of its vertical dive heading generally toward the target. A hydrodynamic scheme is illustrated wherein the center of gravity of the torpedo is moved forward of the center of buoyancy to increase dynamic stability, to allow the use of small fins and control surfaces, to reduce drag and to reduce power requirements. In addition, the torpedo has a DCoperated, sea-water flooded, contra-rotating motor.

United States Patent 1 l-iargett et al.

[ HOMING DEPTH BOMB FOR SEARCHING FOR AN UNDERWATER TARGET [75] Inventors: Richard L. Hargett, Frederick; Samuel A. Humphrey, Silver Spring, both of Md.

[73] Assignee: The United States of America as represented by the Secretary of the Navy 22 Filed: Mar. 24, 1966 21 Appl. No.: 538,897

[52] US. Cl. 102/7, 114/20 R [51] Int. Cl. F42b 19/00 [58] Field of Search 114/20-24; 102/3, 7

[56] References Cited UNITED STATES PATENTS 1,137,222 4/1915 Leon 1l4/2l.l 1,222,630 4/1917 l-lusted.. 1,312,510 8/1919 Baker.... 1,588,932 6/1926 Blair 2,568,433 9/1951 Daly et al. 114/20 June 12, 1973 Boswell 114/20 X Skramstad et al. 1 14/20 X [57] ABSTRACT A vertically searching depth bomb-torpedo is disclosed having at least four passive, side looking hydrophones for searching each horizontal layer of water and determining the approximate direction of a target during the vertical dive of the torpedo and a set of forwardlooking hydrophones for conducting a snaking search when the torpedo pulls out of its vertical dive heading generally toward the target. A hydrodynamic scheme is illustrated wherein the center of gravity of the torpedo is moved forward of the center of buoyancy to increase dynamic stability, to allow the use of small fins and control surfaces, to reduce drag and to reduce power requirements. In addition, the torpedo has a DC- operated, sea-water flooded, contra-rotating motor.

5 Claims, 5 Drawing Figures PAIENIiOm,

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v Richard L. Hargett Samuel A. Humphrey FIG 1 INVENIORS BY AGENT PAIENIEB Jun v 2 ma SHEETZM ENToRs AGENT llf///////H Richard L. Hdrgefl Samuel A. Humphrey all/?! in //%l away/4% virtually any point on the globe. Their detection is at best difficult, and their great mobility and maneuverability further complicate the development of adequate defenses against submarines. As a result, considerable effort has been expended to develop a variety of antisubmarine weapons. These may be roughly divided into two categories according to warhead type: nuclear and non-nuclear or conventional. This is not a merely arbitrary classification made for purposes of convenience. The warhead type is perhaps the greatest single factor controlling the design of the delivery vehicle and its method of deploymenLNuclear anti-submarine weapons are typically delivered over a great distance by a ballistic or semi-ballistic missile. It is important in the use of these weapons that the launching platform be outside the sphere of influence of the warhead when detonation occurs. Obviously, nuclear anti-submarine weapons cannot be safely used against close-in targets. Conventional anti-submarine weapons have, therefore, been developed for use against close-in targets and other situations where it is not practical to use a nuclear anti-submarine weapon. These conventional weapons typically take the form of a search torpedo which is programmed-.to execute a predetermined search maneuver until, the target is acquired by its acoustical sensing system. Thereafter, the torpedo locks onto its target and swims to the kill.

While conventional anti-submarine weapon torpedoes have been developed to a state of fairly high sophistication, a numberof problems yet remain to be solved. Among the greatest of these is the problem of searching quickly for a.target. For example, one type of search torpedo employs a narrow beam acoustical transducer and searches in a slow helical pattern. Another type, which is a little faster, dives to an initial search depth and searches in a flat circle with a broad beam acoustical transducer. Because of reverberation and reflection problems associated with this type of transducer, complex and expensive circuitry are re quired to maintain noise levels at an acceptable minimum. It also leaves a hole in the middle of the search volume which requires the torpedo to run off to one side and look back to completely search the entire volume. The long search times which are characteristic of any of these weapons greatly reduces their kill probabilities.

In addition, conventional torpedoes are rather long and unstreamlined. The reason for this is that for purposes of flight stability watertorpedoes are designed to exhibit a neutral buoyancy. A streamlined shape displaces less water than doesthe conventional shape. As a result, if a streamlined shape were used, either component weights become very critical to maintain-a neutral buoyancy or the torpedo must be driven with an angle of attack to compensate for the unsupported weight. The bulky, unstreamlined shape of conventional torpedoes, while contributing to flight stability, imposes considerable demands on the propulsion system due to its high drag coefficient.

It is therefore an object of the instant invention to provide an anti-submarine weapon which employs a conventional warhead and has an enhanced kill probability due to a much shorter acquisition or search time than heretofore known conventional anti-submarine weapons.

It is another object of this invention to provide a vertically searching, homing depth bomb which is smaller, simpler and less costly to manufacture than presently available search torpedoes.

It is a further object of the invention to provide a homing anti-submarine'weapon which employs a novel hydrodynamic shape and configuration that permits the control surfaces to be very small and significantly reduces the power plant requirement.

It is still another object of this invention to provide in a homing depth bomb a method of searching for an underwater target which results in a much shorter acquisition time than heretofore known.

According to the present invention, the foregoing and other objects are attained by providing a verticallysearching depth bomb having one or more passive, side-looking hydrophones for searching each horizontal layer and determining the approximate direction of a larget during the vertical dive and a forward-looking hydrophone used in conducting a snaking horizontal search when the weapon pulls out of its vertical dive heading in a direction generally towards the target. The homing depth bomb according to the invention has a shape and configuration generally similar to a torpedo but differs therefrom in that it is a slightly streamlined,

- very dense body having a substantially negative buoyancy. The center of gravity of the device is forward of the center of buoyancy thereby increasing dynamic stability and enabling the use of smaller fins and control surfaces than heretofore found necessary. This arrangement results in lower drag and a smaller power requirement. A novel DC-operated, sea-water flooded, contra-rotating motor is employed and has the advantages of low cost and less noise. Additional economies are realized-through theuse of narrow-beam acoustical transducers with their minimum requirement for reverberation elimination which is made possible by the unique search and homing pattern employed by the weapon.

Thespecific nature of the invention, as well as other objects, aspects, uses and advantages thereof, will clearly appear from the accompanying drawing, in which:

FIG. 1 is a pictorial diagram illustrating the search and homing pattern of the homing depth bomb according to the invention;

FIG. 2 is a cross-sectional view of the homing depth bomb showing the physical placement of its various components;

FIG. 3 is a cross-sectional view of the brushless, contra-rotating DC motor used to propel the weapon;

FIG. 4 is a block diagram showing the basic components and their interrelationship of the guidance and control system; and

FIG. 5 illustrates the angular relationships with the inertial reference.

Referring now to the drawings and more particularly to FIG. 1, the homing depth bomb 10, when dropped into the water, sinks rapidly due to its negative buoyancy. The weapon may be delivered to thegeneral area of the traget 11 by any of a variety of means including helicopter, fixed-wing aircraft, and ballistic or semiballistic missile. During the vertical descent the weapon assumes a nose-down attitude due to its center of gravity being forward of its center of buoyancy. Vertical search is accomplished with a plurality (typically four) of passive, side-looking acoustical transducers. The number of transducers required is a function of the rate of descent, spin rate, and the beam width of the acoustical transducer. For example, if the weapon is stabilized against spin, it would be equipped with at least four transducers so that all four quadrants in the horizontal plane would be covered by the transducer beam patterns. In the more general case, however, the weapon is either allowed to spin or a substantial spin rate along its longitudinal axis is induced either prior to its entry into the water or by its hydrodynamic control surfaces. In such case, as few as one side-looking transducer may be employed if the spin rate is sufficiently large with respect to the descent rate. The transducers themselves are the narrow-beam variety thus greatly simplifying the receiving and detection circuitry. Descent is accomplished solely by gravity; therefore, no propulsion is required during the vertical search phase. Since the motor is not running at this time, no noise is generated and the only drain on the power supply is that required for the receiving and detection circuits. The advantages of this no-power" search are many. Since the signal-to-noise ratio is improved, detection circuitry is simplified and detection range is increased. In addition, power supply requirements are reduced. The shaded area in FIG. 1 generally indicates the vertical beam pattern of a passive, side-looking transducer in the homing depth bomb 10. Acoustical-noise generated by the target 11 is detected by the transducer. The weapons motor is then turned on. At this point, indicated by the letter A in the figure, the search phase ends and the recovery or pitch-up phase begins. During the recovery phase, the weapon is stabilized against spin and pitches up generally in the direction of the target following a patch similar to that illustrated between points A and B. Once the weapon has regained the detection depth, it then levels off and begins a snaking search employing its forward looking acoustical transducer as an active search element. This continues until the target is once again acquired. The forward looking transducer then locks onto the target and directs the final homing attack.

As shown in FIG.2 the forward section 12 of the homing depth bomb is pressurized and contains the warhead explosive 13 which may be,-for example, nitranol. Mounted in the flattened nose head of the explosive 13 is the forward looking transducer 14 which is used during the active pursuit phase of the weapons maneuvers. A side-looking transducer 15 is mounted flush in the side of the forward section 12. The guidance and homing package 16 is positioned just aft of the explosive l3 and forward of bulkhead 17 which seals forward section 12. An exloder or detonator 18 which is inserted through the bulkhead 17 extends into and is in intimate contact with explosive 13. Forward section 12 tapers slightly toward the nose. This promotes laminar flow overside-looking transducer 15 further enhancing the signal-to-noise ratio. It also decreases the drag on the weapon skin. The aft section 19 is flooded; that is, sea-water is vented into and flows through this section. Section 19 contains a sea-water battery 20 which is mounted just behind bulkhead l7 and a brushless, counter-rotating DC motor 21 positioned behind battery 20. The sea-water intake and flow control 22 opens through the skin of the weapon between battery 20 and motor 21. Beyond motor 21 is a smooth, tapering low-density section 23 that flares into the hubs of contra-rotating propellers 24 and 25. Section 23 may be, for example, a suitable foam plastic. It is necessary that the tail of the bomb be made as light as possible to shift the center of gravity forward. More specifically the center of gravity in the homing depth bomb is typically 0.3 of the overall length from the nose. The conventional practice in torpedo design is to place the center of gravity at about 0.4 of the length from the nose. Propellers 24 and 25 are driven through shafts 26 by motor 21. The fins and hydrodynamic control surfaces 27 are quite small and are placed just forward of propellers 24 and 25. Due to its extremely short length and semi-streamlined configuration, the homing depth bomb is quite dense having a specific gravity equal to about 1.6. The weapon flies during its homing phase at very high speeds (on the order of 50 knots) at a slight angle of attack (about 2 to 3 degrees). In flight the bomb is highly stable, and very responsive control is had with only'small control forces.

The flooded electric motor 21 is shown in crosssection in FIG. 3. This motor requires no pressure vessel to contain it nor seals on the propeller shafts. The motor comprises a single, generally cylindrically shaped stator 28. Stator 28 is hollow and surrounds an inner armature 29 coaxially aligned therewith and which is rotatably supported by thrust bearing 30 at one end of the stator. An outer, coaxial armature 31 surrounds stator 28 and is rotatably supported by thrust bearing 32 at the other end of the stator. Two hollow, coaxial propeller shafts are integrally formed with the armatures; inner shaft 33 being formed with armature 29, and outer shaft 34, with armature 31. The shafts 33 and 34 are directly connected with propellers 25 and 24, respectively (shown in FIG. 2). Since annatures 29 and 31 see oppositely rotating electric fields, they rotate in opposite directions. This eliminates the need for a gear box which is a prime contributor to weight, noise and cost of manufacture. A housing 35, which supports stator 28 and may be conveniently formed integrally therewith, encloses the stator and double armature assembly. ,Since the motor is flooded, normal brush-type commutation is obviously impractical. Commutation is here provided by a unique photoelectric switching arrangement. This arrangement comprises a light source 36 supported within the housing along the axis of and ahead of the'stator-armature assembly. A hollow, cylindrical sleeve 37 integrally formed with armature 29 axially rotates about light source 36. A plurality of photo diodes 38 supported by housing 35 without sleeve 37 are aligned with light source 36 in a plane perpendicular to the motor axis. An aperture 48 sequentially exposes photo diodes 38 to radiation from light source 36 as armature 29 rotates. Sea-water vented into the weapon through intake and flow control 22 (shown in FIG. 2) enters motor 21 through ports 39, travels through armature 29 and exhausts through propeller shaft 33.

FIG. 4 shows the block diagram of the guidance and control package 16. This system comprises three basic groupings of elements: the control sensors, the programmer and pitch converter, and the control converter and autopilot. The control sensors may be divided into the gyro package and inertial sensors 40 and the hydrostatic sensor 43. The gyro package and inertial sensors 40 provide body rates, and of, about the pitch and yaw axes, respectively, with respect to the roll axis which is stabilized against body spin. The roll axis is maintained fixed inertially to provide an angular reference, r,,,, as illustrated in FIG. 5, for the pitch axis of the weapon. This angular reference and its first derivative, r or spin rate, are also provided by the gyro package and inertial sensors 40. The programmer 41 uses the angular body inertial reference, r and the body target angle, r derived from the side-looking acoustical sensor 42 to obtain a total angle, R to the target from the fixed inertial reference axis. The fixed pitch-up maneuver contained in programmer 41 together with the depth signal derived from depth sensor 43 are resolved about this angle. The component signals thus derived are mixed with the angular rates, 0, and 0,,, from the gyro package and inertial sensors 40 and integrated by the pitch converter 44 to provide rate and position control about the inertial axes to the control converter 45. The control converter 45 also receives body-inertial angular reference r and resolves the inertial rate and position controls into yaw and pitch controls which are supplied to the autopilot 46. This information and an appropriate vehicle transfer function are utilized by the autopilot 46 to provide power signals to the weapon control surfaces. Thus, once the side acoustical sensor 42 has identified a target and the quadrant, the programmer 41 turns the power plant on and utilizes a fixed pitch program to rotate the weapon 90 degrees up in the direction of the target and bring the weapon to target depth. A programmed snake search is then employed by the programmer to facilitatetarget scan and acquisition by the forward looking acoustical sensor 47. Thereafter, the forward looking sensor 47 is used to home the weapon into the target by providing target azimuth and elevation information directly to autopilot 46.

It will be apparent that the embodiment shown is only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

We claim as our invention:

1. A vertically diving searching homing depth bomb comprising:

a forward section having a flat blunt nose and containing the warhead explosive,

a forward looking transducer mounted in the nose of said forward section,

at least one side-looking transducer mounted flush in the side of said forward section,

a guidance and homing package positioned just aft of said warhead explosive in said forward section, said forward section tapering toward its nose to promote laminar flow over said side-looking transducer thereby enhancing the signal-to-noise ratio of said side-looking transducer and decreasing the drag on the weapon skin,

an aft section mating smoothly with said forward section and tapering to a minimum diameter, and

a propulsion system contained in said aft section.

2. A vertically diving searching, homing depth bomb as recited in claim 1 having a substantially negative buoyancy and its center of gravity located forward of its center of buoyancy.

3. A vertically diving and searching homing depth bomb having a substantially negative buoyancy and its center of gravity located forward of its center of buoyancy comprising:

a forward section having a flat blunt nose and containing a warhead explosive;

a forward looking transducer mounted in the nose of said forward section;

at least one side-looking transducer mounted flush in the side of said forward section;

a guidance and homing package positioned just aft of said warhead explosive in said forward section;

' said forward section tapering toward its nose to promote laminar flow over said side-looking transducer thereby enhancing the signal-to-noise ratio of said side-looking transducer and decreasing the drag on the weapon skin;

an aft section mating smoothly with said forward section and tapering to a minimum diameter; and

a propulsion system contained in said aft section, said propulsion system including a sea-water battery, and a DC-operated, sea-water flooded, contrarotating motor.

4. A vertically diving and searching homing depth bomb as recited in claim 3 wherein said DC-operated, sea-water flooded, contra-rotating motor comprises:

a single, generally cylindrically shaped, hollow stator;

an inner armature positioned within said stator and coaxially aligned therewith, said inner armature being rotatably supported at one end of said stator; an outer, coaxial armature surrounding said stator and rotatably supported at the other end thereof;

a housing supporting said stator and enclosing the stator and double armature assembly; and

a brushless commutating system supported by said housing and driven by one of said armatures.

5. A vertically diving and searching homing depth bomb as recited in claim 4 wherein said brushless commutating system comprises:

a light source supported within said housing along the axis of an ahead of the stator armature assembly;

a hollow cylindrical sleeve connected to said inner armature and surrounding said light source, and sleeve having an aperture cut therein; and

a plurality of photo diodes supported by said housing without said sleeve and aligned with said light source in a plane perpendicular to the motor axis whereby each of said photo diodes is sequentially exposed to radiation from said light source through said aperture as said inner armature rotates. 

1. A vertically diving searching homing depth bomb comprising: a forward section having a flat blunt nose and containing the warhead explosive, a forward looking transducer mounted in the nose of said forward section, at least one side-looking transducer mounted flush in the side of said forward section, a guidance and homing package positioned just aft of said warhead explosive in said forward section, said forward section tapering toward its nose to promote laminar flow over said side-looking transducer thereby enhancing the signal-to-noise ratio of said side-looking transducer and decreasing the drag on the weapon skin, an aft section mating smoothly with said forward section and tapering to a minimum diameter, and a propulsion system contained in said aft section.
 2. A vertically diving searching, homing depth bomb as recited in claim 1 having a substantially negative buoyancy and its center of gravity located forward of its center of buoyancy.
 3. A vertically diving and searching homing depth bomb having a substantially negative buoyancy and its center of gravity located forward of its center of buoyancy comprising: a forward section having a flat blunt nose and containing a warhead explosive; a forward looking transducer mounted in the nose of said forward section; at least one side-looking transducer mounted flush in the side of said forward section; a guidance and homing package positioned just aft of said warhead explosive in said forward section; said forward section tapering toward its nose to promote laminar flow over said side-looking transducer thereby enhancing the signal-to-noise ratio of said side-looking transducer and decreasing the drag on the weapon skin; an aft section mating smoothly with said forward section and tapering To a minimum diameter; and a propulsion system contained in said aft section, said propulsion system including a sea-water battery, and a DC-operated, sea-water flooded, contra-rotating motor.
 4. A vertically diving and searching homing depth bomb as recited in claim 3 wherein said DC-operated, sea-water flooded, contra-rotating motor comprises: a single, generally cylindrically shaped, hollow stator; an inner armature positioned within said stator and coaxially aligned therewith, said inner armature being rotatably supported at one end of said stator; an outer, coaxial armature surrounding said stator and rotatably supported at the other end thereof; a housing supporting said stator and enclosing the stator and double armature assembly; and a brushless commutating system supported by said housing and driven by one of said armatures.
 5. A vertically diving and searching homing depth bomb as recited in claim 4 wherein said brushless commutating system comprises: a light source supported within said housing along the axis of an ahead of the stator armature assembly; a hollow cylindrical sleeve connected to said inner armature and surrounding said light source, and sleeve having an aperture cut therein; and a plurality of photo diodes supported by said housing without said sleeve and aligned with said light source in a plane perpendicular to the motor axis whereby each of said photo diodes is sequentially exposed to radiation from said light source through said aperture as said inner armature rotates. 